1. Field of the Invention
This invention relates to a process for the preparation of 2,3-dimethylpentanal. More especially, this invention relates to an improved process for the preparation of 2,3-dimethylpentanal via hydroformylation of 3-methyl-2-pentene employing a rhodium carbonyl catalyst. The catalyst employed according to the process of the invention is one consisting essentially of rhodium, carbon monoxide and in certain cases, hydrogen.
1. Discussion of the Prior Art
According to the process described in U.S. Pat. No. 3,359,324, 2,3-dimethylpentanal can be manufactured from crotonaldehyde. The synthesis is multi-stage. Crotyl alcohol, propionaldehyde dicrotyl acetal and 1-propenyl-crotyl ether result as intermediate compounds.
The reaction of methyl sec-butyl ketone with monochlorodimethyl ether to 1-methoxy-2,3-dimethyl-2-pentanal and the subsequent hydrolysis of the methoxyaldehyde with hydrochloric acid also result in 2,3-dimethylpentanal (French Pat. No. 1,377,141).
The manufacture of 2,3-dimethylpentanal via hydroformylation of 3-methyl-1-pentene is described by P. Pino et al in "Chemistry and Industry", 1963, p. 294. When cobalt carbonyl is employed as catalyst, a reaction product containing 93% 4-methylhexanal but only 3% 2,3-dimethylpentanal is obtained.
With the hydroformylation of 3-methyl-2-pentene in the presence of hydridocarbonyltris (triphenylphosphine) rhodium, a reaction product with an 85-86% 2,3-dimethylpentanal content is obtained with a 50% olefin conversion. (Stefani et al, Journal of American Chemical Society, 95: 19, 6504, 1973).
Consequently, the known processes for the synthesis of 2,3-dimethylvaleraldehyde require either a multi-stage procedure or they result, in the case of less complex reactions, in unsatisfactory yields of the required compound. The application of rhodium carbonyls (containing phosphine) is confronted by the high cost of this catalyst, as its separation in undecomposed form from the reaction product is highly involved. Moreover, the olefin conversion with this special catalyst system is very small.
It is an object of this invention, therefore, to provide a process for the economical preparation of 2,3-dimethylpentanal. More especially, it is an object of this invention to provide an economical process by which 2,3-dimethylpentanal can be prepared on an industrial scale through the hydroformylation of 3-methyl-2-pentene. It is a further object of this invention, therefore, to provide an improved process for the hydroformylation of 3-methyl-2-pentene by which high yields of 2,3-dimethylpentanal are realized. These and other objects of this invention will become apparent from the following description and claims.